This invention relates generally to a pinion support and, more particularly, to an improved bearing configuration for supporting a hollow pinion in an axle assembly.
Certain vehicle applications benefit from a drive axle configuration that uses a gear assembly having a hollow pinion gear used in combination with a through shaft. The shaft passes through a bore in the pinion to coaxially transfer power to another area in the vehicle drivetrain. One example of an application that can benefit from this type of gear arrangement is a tandem drive axle set.
A tandem drive axle set is used to distribute rotational power from a driveline input to a set of forward and rear wheels through a forward drive axle assembly and a rear drive axle assembly, respectively. Traditionally, the tandem drive axle set is designed such that the forward drive axle assembly has a ring gear and a pinion gear set that is a mirror image of the rear drive axle assembly ring gear and pinion gear set. Usually, the forward drive axle assembly has a right-hand pinion gear while the rear drive axle assembly has a left-hand pinion gear. It is necessary that the forward and rear drive axle assemblies be mirror images of each other because, traditionally, the forward drive axle assembly has included a set of helical gears that are used to transfer half of the rotational power from an inter-axle differential to the forward drive axle assembly pinion and ring gear set.
The inter-axle differential receives rotational input from the driveline of the vehicle. In such a design, the pinion gear of the forward drive axle assembly rotates in the opposite direction to that of the inter-axle differential. The inter-axle differential transmits the other half of its input to a through shaft, which sends the input back to the rear drive axle assembly. In the rear drive axle assembly the pinion gear rotates in the same direction as the inter-axle differential. Because the helical gears are necessary in the forward drive axle assembly, the axis of the input to the forward drive axle assembly is offset from the pinion gear axis in the forward drive axle assembly by the centerline-to-centerline distance of the helical gears. Therefore, the output of the forward drive axle assembly is on the same axis as the input while the input of the rear drive axle assembly is on the same axis as the forward drive axle pinion gear.
This difference in axis height between the forward axle output to the rear axle input requires different axle pinion angles to be utilized in order to set the driveline angles in the u-joints used in the driveline. Setting and maintaining the driveline angles is difficult. When the driveline angles at the u-joints arc not the same it creates adverse torsional loading and vibrations in the drivetrain assembly. Such torsional loading and vibrations can lead to premature failure of the drivetrain assembly. Even when the driveline angles are properly set at the factory, the air-ride suspensions commonly found in heavy duty trucks can alter the driveline working angles in an adverse manner.
As discussed above, the hollow pinion gear configuration solves this problem by providing coaxial power transfer from the forward drive axle to the rear drive axle. This configuration is further described in U.S. Pat. No. 6,200,240 assigned to the assignee of the present invention. The through shaft extends from the inter-axle differential and through the hollow pinion gear. The hollow pinion gear drives the main differential in the forward drive axle assembly. The through shaft extends toward the rear drive axle assembly which utilizes a traditional pinion gear to drive a rear differential. This configuration allows a common axis to be shared by the input to the forward drive axle assembly and the input to the rear drive axle assembly.
One disadvantage with this configuration is that the bearing journals formed on the hollow pinion shaft can be difficult to machine. The hollow pinion shaft has a first bearing journal portion on an inboard end of the shaft and a second bearing journal portion on an outboard end of the shaft. A toothed pinion gear head is formed on the shaft between the first and second bearing journals. Because the first bearing journal portion is positioned close to the pinion gear head, the first bearing journal portion can become mutilated during the gear cutting process, i.e. too much material can inadvertently be removed from this first bearing journal area. This can reduce the strength of this bearing journal, which is undesirable. Further, the mutilation of the bearing journal portion will result in increased scrap rates for the hollow pinion shafts, which can significantly increase costs.
Thus, it is desirable to provide an improved hollow pinion support configuration that eliminates bearing journal machining problems. The improved bearing configuration should be capable of providing similar strength, fatigue life, and operation performance during vehicle operation as the traditional configuration.